In the treatment of diseases, injuries, or malformations affecting spinal motion segments, and especially those affecting disc tissue, it has long been known to remove some or all of a degenerated, ruptured, or otherwise failing disc. In cases involving intervertebral disc tissue that has been removed or is otherwise absent from a spinal motion segment, corrective measures are taken to ensure the proper spacing of the vertebrae formerly separated by the removed disc tissue. In some instances, prosthetic devices are inserted into the disc space to maintain the structural integrity of the spinal column.
Insertion of prosthetic devices has heretofore been accomplished from an anterior approach to the vertebrae. However, in some regions of the spine, correction from the anterior approach may present difficulties due to the presence of important anatomical structures such as vessels and nerves. For example, the straight anterior approach to the disc space between vertebra L4 and L5, as well as the superior disc levels, can present high surgical risks during the insertion of an implant such as an artificial disc or prosthetic device because of the attachment of the major vessels to the anterior aspect of the spine. Alternatives to correction from an anterior approach are therefore desirable.
Moreover, subsidence of prosthetic devices into adjacent vertebrae has often been a problem due to insufficient contact between the prosthetic device and the appropriate bearing surface provided by the adjacent vertebrae. For example, subsidence of the prosthetic device into the adjacent vertebrae may occur, which can result in a decreased amount of support offered by the prosthetic device. Often, such subsidence is caused by the surgical instruments and/or methods used for inserting the prosthetic device. Surgical instruments often cause or require invasion of the vertebrae and/or other parts of the patient beyond the level of invasion required for the implant itself. For example, the surgical instrument may require removal of additional portions of the vertebral bodies, which can reduce the ingrowth and contact areas and compromise the structural integrity of the vertebral body.
Therefore, what is needed is a surgical instrument for inserting an artificial intervertebral prosthetic device that is simple, stable, and does not compromise the advantages of the artificial intervertebral prosthetic device. Furthermore, what is needed is minimally invasive instrumentation which can be inserted from different approaches. Furthermore, an artificial intervertebral prosthetic device and corresponding instrumentation is needed whereby the window associated with the insertion of the disc is minimized and the bearing contact between the device and the adjacent vertebrae is maximized.